<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        var wid = 'a50px';
        //NaN  not a number
        //parseFloat(wid)  50
        wid = parseFloat(wid) + 100 + 'px';
        console.log(wid)

        /*
          parseInt(var)
        – parseFloat(var)
        – Number(var)
         */
    </script>
</head>
<body>

</body>
</html>